391 lines
12 KiB
C++
391 lines
12 KiB
C++
/*!
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* @file DHT.cpp
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*
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* @mainpage DHT series of low cost temperature/humidity sensors.
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*
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* @section intro_sec Introduction
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*
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* This is a library for DHT series of low cost temperature/humidity sensors.
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*
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* You must have Adafruit Unified Sensor Library library installed to use this
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* class.
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*
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* Adafruit invests time and resources providing this open source code,
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* please support Adafruit andopen-source hardware by purchasing products
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* from Adafruit!
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*
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* @section author Author
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*
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* Written by Adafruit Industries.
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*
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* @section license License
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*
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* MIT license, all text above must be included in any redistribution
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*/
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#include "DHT.h"
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#define MIN_INTERVAL 2000 /**< min interval value */
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#define TIMEOUT \
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UINT32_MAX /**< Used programmatically for timeout. \
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Not a timeout duration. Type: uint32_t. */
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/*!
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* @brief Instantiates a new DHT class
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* @param pin
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* pin number that sensor is connected
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* @param type
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* type of sensor
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* @param count
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* number of sensors
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*/
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DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
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(void)count; // Workaround to avoid compiler warning.
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_pin = pin;
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_type = type;
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#ifdef __AVR
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_bit = digitalPinToBitMask(pin);
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_port = digitalPinToPort(pin);
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#endif
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_maxcycles =
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microsecondsToClockCycles(1000); // 1 millisecond timeout for
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// reading pulses from DHT sensor.
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// Note that count is now ignored as the DHT reading algorithm adjusts itself
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// based on the speed of the processor.
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}
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/*!
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* @brief Setup sensor pins and set pull timings
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* @param usec
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* Optionally pass pull-up time (in microseconds) before DHT reading
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*starts. Default is 55 (see function declaration in DHT.h).
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*/
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void DHT::begin(uint8_t usec) {
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// set up the pins!
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pinMode(_pin, INPUT_PULLUP);
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// Using this value makes sure that millis() - lastreadtime will be
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// >= MIN_INTERVAL right away. Note that this assignment wraps around,
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// but so will the subtraction.
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_lastreadtime = millis() - MIN_INTERVAL;
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DEBUG_PRINT("DHT max clock cycles: ");
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DEBUG_PRINTLN(_maxcycles, DEC);
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pullTime = usec;
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}
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/*!
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* @brief Read temperature
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* @param S
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* Scale. Boolean value:
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* - true = Fahrenheit
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* - false = Celcius
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* @param force
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* true if in force mode
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* @return Temperature value in selected scale
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*/
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float DHT::readTemperature(bool S, bool force) {
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float f = NAN;
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if (read(force)) {
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switch (_type) {
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case DHT11:
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f = data[2];
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if (data[3] & 0x80) {
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f = -1 - f;
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}
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f += (data[3] & 0x0f) * 0.1;
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if (S) {
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f = convertCtoF(f);
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}
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break;
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case DHT12:
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f = data[2];
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f += (data[3] & 0x0f) * 0.1;
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if (data[2] & 0x80) {
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f *= -1;
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}
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if (S) {
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f = convertCtoF(f);
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}
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break;
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case DHT22:
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case DHT21:
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f = ((word)(data[2] & 0x7F)) << 8 | data[3];
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f *= 0.1;
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if (data[2] & 0x80) {
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f *= -1;
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}
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if (S) {
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f = convertCtoF(f);
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}
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break;
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}
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}
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return f;
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}
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/*!
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* @brief Converts Celcius to Fahrenheit
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* @param c
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* value in Celcius
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* @return float value in Fahrenheit
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*/
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float DHT::convertCtoF(float c) { return c * 1.8 + 32; }
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/*!
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* @brief Converts Fahrenheit to Celcius
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* @param f
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* value in Fahrenheit
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* @return float value in Celcius
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*/
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float DHT::convertFtoC(float f) { return (f - 32) * 0.55555; }
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/*!
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* @brief Read Humidity
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* @param force
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* force read mode
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* @return float value - humidity in percent
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*/
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float DHT::readHumidity(bool force) {
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float f = NAN;
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if (read(force)) {
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switch (_type) {
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case DHT11:
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case DHT12:
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f = data[0] + data[1] * 0.1;
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break;
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case DHT22:
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case DHT21:
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f = ((word)data[0]) << 8 | data[1];
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f *= 0.1;
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break;
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}
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}
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return f;
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}
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/*!
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* @brief Compute Heat Index
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* Simplified version that reads temp and humidity from sensor
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* @param isFahrenheit
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* true if fahrenheit, false if celcius
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*(default true)
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* @return float heat index
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*/
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float DHT::computeHeatIndex(bool isFahrenheit) {
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float hi = computeHeatIndex(readTemperature(isFahrenheit), readHumidity(),
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isFahrenheit);
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return hi;
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}
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/*!
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* @brief Compute Heat Index
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* Using both Rothfusz and Steadman's equations
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* (http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml)
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* @param temperature
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* temperature in selected scale
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* @param percentHumidity
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* humidity in percent
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* @param isFahrenheit
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* true if fahrenheit, false if celcius
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* @return float heat index
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*/
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float DHT::computeHeatIndex(float temperature, float percentHumidity,
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bool isFahrenheit) {
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float hi;
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if (!isFahrenheit)
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temperature = convertCtoF(temperature);
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hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) +
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(percentHumidity * 0.094));
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if (hi > 79) {
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hi = -42.379 + 2.04901523 * temperature + 10.14333127 * percentHumidity +
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-0.22475541 * temperature * percentHumidity +
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-0.00683783 * pow(temperature, 2) +
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-0.05481717 * pow(percentHumidity, 2) +
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0.00122874 * pow(temperature, 2) * percentHumidity +
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0.00085282 * temperature * pow(percentHumidity, 2) +
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-0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
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if ((percentHumidity < 13) && (temperature >= 80.0) &&
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(temperature <= 112.0))
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hi -= ((13.0 - percentHumidity) * 0.25) *
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sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);
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else if ((percentHumidity > 85.0) && (temperature >= 80.0) &&
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(temperature <= 87.0))
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hi += ((percentHumidity - 85.0) * 0.1) * ((87.0 - temperature) * 0.2);
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}
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return isFahrenheit ? hi : convertFtoC(hi);
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}
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/*!
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* @brief Read value from sensor or return last one from less than two
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*seconds.
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* @param force
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* true if using force mode
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* @return float value
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*/
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bool DHT::read(bool force) {
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// Check if sensor was read less than two seconds ago and return early
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// to use last reading.
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uint32_t currenttime = millis();
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if (!force && ((currenttime - _lastreadtime) < MIN_INTERVAL)) {
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return _lastresult; // return last correct measurement
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}
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_lastreadtime = currenttime;
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// Reset 40 bits of received data to zero.
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data[0] = data[1] = data[2] = data[3] = data[4] = 0;
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#if defined(ESP8266)
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yield(); // Handle WiFi / reset software watchdog
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#endif
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// Send start signal. See DHT datasheet for full signal diagram:
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// http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
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// Go into high impedence state to let pull-up raise data line level and
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// start the reading process.
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pinMode(_pin, INPUT_PULLUP);
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delay(1);
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// First set data line low for a period according to sensor type
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pinMode(_pin, OUTPUT);
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digitalWrite(_pin, LOW);
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switch (_type) {
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case DHT22:
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case DHT21:
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delayMicroseconds(1100); // data sheet says "at least 1ms"
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break;
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case DHT11:
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default:
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delay(20); // data sheet says at least 18ms, 20ms just to be safe
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break;
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}
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uint32_t cycles[80];
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{
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// End the start signal by setting data line high for 40 microseconds.
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pinMode(_pin, INPUT_PULLUP);
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// Delay a moment to let sensor pull data line low.
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delayMicroseconds(pullTime);
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// Now start reading the data line to get the value from the DHT sensor.
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// Turn off interrupts temporarily because the next sections
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// are timing critical and we don't want any interruptions.
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InterruptLock lock;
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// First expect a low signal for ~80 microseconds followed by a high signal
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// for ~80 microseconds again.
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if (expectPulse(LOW) == TIMEOUT) {
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DEBUG_PRINTLN(F("DHT timeout waiting for start signal low pulse."));
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_lastresult = false;
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return _lastresult;
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}
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if (expectPulse(HIGH) == TIMEOUT) {
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DEBUG_PRINTLN(F("DHT timeout waiting for start signal high pulse."));
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_lastresult = false;
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return _lastresult;
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}
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// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
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// microsecond low pulse followed by a variable length high pulse. If the
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// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
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// then it's a 1. We measure the cycle count of the initial 50us low pulse
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// and use that to compare to the cycle count of the high pulse to determine
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// if the bit is a 0 (high state cycle count < low state cycle count), or a
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// 1 (high state cycle count > low state cycle count). Note that for speed
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// all the pulses are read into a array and then examined in a later step.
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for (int i = 0; i < 80; i += 2) {
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cycles[i] = expectPulse(LOW);
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cycles[i + 1] = expectPulse(HIGH);
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}
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} // Timing critical code is now complete.
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// Inspect pulses and determine which ones are 0 (high state cycle count < low
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// state cycle count), or 1 (high state cycle count > low state cycle count).
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for (int i = 0; i < 40; ++i) {
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uint32_t lowCycles = cycles[2 * i];
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uint32_t highCycles = cycles[2 * i + 1];
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if ((lowCycles == TIMEOUT) || (highCycles == TIMEOUT)) {
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DEBUG_PRINTLN(F("DHT timeout waiting for pulse."));
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_lastresult = false;
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return _lastresult;
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}
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data[i / 8] <<= 1;
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// Now compare the low and high cycle times to see if the bit is a 0 or 1.
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if (highCycles > lowCycles) {
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// High cycles are greater than 50us low cycle count, must be a 1.
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data[i / 8] |= 1;
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}
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// Else high cycles are less than (or equal to, a weird case) the 50us low
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// cycle count so this must be a zero. Nothing needs to be changed in the
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// stored data.
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}
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DEBUG_PRINTLN(F("Received from DHT:"));
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DEBUG_PRINT(data[0], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[1], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[2], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[3], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[4], HEX);
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DEBUG_PRINT(F(" =? "));
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DEBUG_PRINTLN((data[0] + data[1] + data[2] + data[3]) & 0xFF, HEX);
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// Check we read 40 bits and that the checksum matches.
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if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
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_lastresult = true;
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return _lastresult;
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} else {
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DEBUG_PRINTLN(F("DHT checksum failure!"));
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_lastresult = false;
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return _lastresult;
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}
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}
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// Expect the signal line to be at the specified level for a period of time and
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// return a count of loop cycles spent at that level (this cycle count can be
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// used to compare the relative time of two pulses). If more than a millisecond
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// ellapses without the level changing then the call fails with a 0 response.
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// This is adapted from Arduino's pulseInLong function (which is only available
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// in the very latest IDE versions):
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// https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/wiring_pulse.c
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uint32_t DHT::expectPulse(bool level) {
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// F_CPU is not be known at compile time on platforms such as STM32F103.
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// The preprocessor seems to evaluate it to zero in that case.
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#if (F_CPU > 16000000L) || (F_CPU == 0L)
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uint32_t count = 0;
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#else
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uint16_t count = 0; // To work fast enough on slower AVR boards
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#endif
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// On AVR platforms use direct GPIO port access as it's much faster and better
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// for catching pulses that are 10's of microseconds in length:
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#ifdef __AVR
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uint8_t portState = level ? _bit : 0;
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while ((*portInputRegister(_port) & _bit) == portState) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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}
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// Otherwise fall back to using digitalRead (this seems to be necessary on
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// ESP8266 right now, perhaps bugs in direct port access functions?).
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#else
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while (digitalRead(_pin) == level) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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}
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#endif
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return count;
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}
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